1. Field of the Invention
The invention relates to an assembled battery in which a plurality of chargeable/dischargeable electric unit cells (secondary cells) are connected in series. Specifically, the invention relates to an assembled battery that is suitable to be mounted in a vehicle, and also relates to a structure of a unit cell that constitutes the assembled battery, and to a vehicle in which the assembled battery is mounted.
2. Description of the Related Art
Assembled batteries formed by connecting in series a plurality of unit cells, such as lithium-ion cells, nickel hydride cells, other secondary cells, or electric storage elements, such as capacitors or the like, are rising in importance as high-output electric power sources for use as vehicle-mounted electric power sources, or electric power sources of personal computers or portable communication terminals. Particularly, an assembled battery formed by series-connecting a plurality of lithium-ion cells as unit cells that are light in weight but capable of providing high energy density is expected to be favorably used as a vehicle-mounted high-output electric power source.
In this kind of assembled battery constructed of a plurality of unit cells, heat is produced within each of the unit cells constituting the assembled battery when the assembled battery is charged or discharged. Therefore, it is required that the assembled battery certainly have a heat dissipation characteristic so as to rapidly release the produced heat and thus cool off. A proposed related-art technique that meets the requirement is a technique in which cooling wind passageways are provided between adjacent unit cells to better the heat dissipation characteristic of the assembled battery (e.g., in Japanese Patent Application Publication No. 2006-260967 (JP-A-2006-260967)). Other examples of the related art include those described in Japanese Patent Application Publication No. 9-199179 (JP-A-9-199179), Japanese Patent Application Publication No. 2001-57196 (JP-A-2001-57196), and Japanese Patent Application Publication No. 2005-116438 (JP-A-2005-116438).
By the way, since the assembled battery mounted in a vehicle, such as a motor vehicle or the like, is provided on the assumption of the use in a vibrating environment in addition to the limited mounting space, the vehicle-mounted assembled battery is constructed with many unit cells being arranged and constrained (i.e., unit cells being fastened to each other). At the time of constraining the unit cells that constitute an assembled battery, a considerable load is applied to each unit cell.
The considerable load applied at the time of the constraining process gives rise to a problem of a cell container body (i.e., an exterior body that houses electrode bodies and an electrolyte) bending or deforming in the direction of load. The distortion of the container body becomes a factor of the deviation and variation of the distance (dimension) or the relative position between the positive and negative electrode terminals of each unit cell that are to be connected in series from the initially designed ideal values, and is therefore not preferable.
Although it may be considered appropriate to use a thick-walled container made of a hard-to-deform material in order to solve the foregoing problem, the thick-walled container made of such a material is not desirable from the standpoint of weight reduction of the assembled battery. Besides, it does not suffice to simply prevent deformation of the container, but it is also necessary to secure sufficient heat dissipation characteristic of the assembled battery.